What does it mean to accelerate anyway?? TO ACCELERATE YOU MUST CHANGE YOUR VELOCITY!! VELOCITY CHANGES IF…. 1. Increase Speed 2. Decrease Speed 3. Change Direction Acceleration- rate at which velocity changes over time; an object accelerates if its speed, direction, or both change -any change in velocity Why? Because velocity includes speed and direction

Change in Velocity Each time you take a step you are changing the velocity of your body. You are probably most familiar with the velocity changes of a moving bus or car. The rate at which velocity (speed or direction) changes occur is called acceleration.

Acceleration Equations Acceleration= final velocity- starting velocity time Change in velocity = final – starting velocity velocity Acceleration= change in velocity time Acceleration = ∆velocity time SI units for acceleration = m/s 2, mi/h 2, km/h 2

When is it positive or negative acceleration? *small acceleration → means speed is ↑ slowly *large acceleration → means speed is ↑ rapidly + acceleration- velocity is ↑ (obj. speeding up) -ex. Pressing on gas pedal in a car - acceleration- velocity is ↓ (obj. slowing down) -ex. Pressing on the brake pedal in a car Important- acceleration does not always mean “speeding up” b/c it’s any change in velocity

Positive acceleration Negative acceleration

- A constant acceleration produces a straight line or linear slope (rise/run). - The slope of a non-linear velocity-time graph (rise/run) will predict an objects instantaneous acceleration. a = v/t

Acceleration = Velocity (final) - Velocity (original) time A car traveling at 60 m/s accelerates to 90 m/s in 3 seconds. What is the car’s acceleration? = 90 m/s - 60 m/s 3 seconds = 30 m/s 3 seconds = 10 m/s 2

Acceleration = Velocity (final) - Velocity (original) time A car traveling at 60 m/s slams on the breaks to avoid hitting a deer. The car comes to a safe stop 6 seconds after applying the breaks. What is the car’s acceleration? = 0 m/s - 60 m/s 6 seconds = - 60 m/s 6 seconds = - 10 m/s 2